Storage controllers with dynamic WWN storage modules and methods for managing data and connections between a host and a storage device

ABSTRACT

A method and system for transferring data between a host and a Serial Attached Small Computer Interface (“SAS”) device using a storage controller is provided. The storage controller includes, a World Wide Name (“WWN”) module that includes a table having plural entries, wherein each row includes a WWN address, an initiator tag value field, an input/output counter value that tracks plural commands for a connection. A WWN index value represents the address of a row having plural entries. The method includes, comparing frame elements of incoming frames, including a unique WWN address with the WWN module entries; and if there is a match, updating a counter value for a connection between the storage controller and a device sending frames. The counter value is increased when a command frame is received and decreased when a command is executed and a response is sent to the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to storage device controllers,and more particularly, to efficiently managing data flow using a WWNmodule.

2. Background

Conventional computer systems typically include several functionalcomponents. These components may include a central processing unit(CPU), main memory, input/output (“I/O”) devices, and streaming storagedevices (for example, tape drives/disks) (referred to herein as “storagedevice”).

In conventional systems, the main memory is coupled to the CPU via asystem bus or a local memory bus. The main memory is used to provide theCPU access to data and/or program information that is stored in mainmemory at execution time. Typically, the main memory is composed ofrandom access memory (RAM) circuits. A computer system with the CPU andmain memory is often referred to as a host system.

The storage device is coupled to the host system via a controller thathandles complex details of interfacing the storage device to the hostsystem. Communications between the host system and the controller isusually provided using one of a variety of standard I/O bus interfaces.

Typically, when data is read from a storage device, a host system sendsa read command to the controller, which stores the read command into abuffer memory. Data is read from the device and stored in the buffermemory.

Various standard interfaces are used to move data from host systems tostorage devices. Fibre channel is one such standard. Fibre channel(incorporated herein by reference in its entirety) is an AmericanNational Standard Institute (ANSI) set of standards, which provides aserial transmission protocol for storage and network protocols such asHIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/outputinterface to meet the requirements of both channel and network users.

Host systems often communicate with storage systems using the standard“PCI” bus interface. PCI stands for Peripheral Component Interconnect, alocal bus standard that was developed by Intel Corporation®. The PCIstandard is incorporated herein by reference in its entirety. Mostmodern computing systems include a PCI bus in addition to a more generalexpansion bus (e.g. the ISA bus). PCI is a 64-bit bus and can run atclock speeds of 33 or 66 MHz.

PCI-X is a standard bus that is compatible with existing PCI cards usingthe PCI bus. PCI-X improves the data transfer rate of PCI from 132 MBpsto as much as 1 GBps. The PCI-X standard (incorporated herein byreference in its entirety) was developed by IBM®, Hewlett PackardCorporation® and Compaq Corporation® to increase performance of highbandwidth devices, such as Gigabit Ethernet standard and Fibre ChannelStandard, and processors that are part of a cluster.

The iSCSI standard (incorporated herein by reference in its entirety) isbased on Small Computer Systems Interface (“SCSI”), which enables hostcomputer systems to perform block data input/output (“I/O”) operationswith a variety of peripheral devices including disk and tape devices,optical storage devices, as well as printers and scanners.

A traditional SCSI connection between a host system and peripheraldevice is through parallel cabling and is limited by distance and devicesupport constraints. For storage applications, iSCSI was developed totake advantage of network architectures based on Fibre Channel andGigabit Ethernet standards. iSCSI leverages the SCSI protocol overestablished networked infrastructures and defines the means for enablingblock storage applications over TCP/IP networks. iSCSI defines mappingof the SCSI protocol with TCP/IP. The iSCSI architecture is based on aclient/server model. Typically, the client is a host system such as afile server that issues a read or write command. The server may be adisk array that responds to the client request.

Serial ATA (“SATA”) is another standard, incorporated herein byreference in its entirety that has evolved from the parallel ATAinterface for storage systems. SATA provides a serial link with apoint-to-point connection between devices and data transfer can occur at150 megabytes per second.

Another standard that has been developed is Serial Attached SmallComputer Interface (“SAS”), incorporated herein by reference in itsentirety. The SAS standard allows data transfer between a host systemand a storage device. SAS provides a disk interface technology thatleverages SCSI, SATA, and fibre channel interfaces for data transfer.SAS uses a serial, point-to-point topology to overcome the performancebarriers associated with storage systems based on parallel bus orarbitrated loop architectures.

The SAS specification addresses all devices in its domain by using aWorld Wide Name (WWN) address. The WWN is a unique 64-bit field that isallocated by IEEE to storage devices manufacturers.

In a SAS domain there could be up to 256 active devices. The devicescould be of Initiator type or Target type. Initiator device initiates anInput/Output process (I/O) by sending a Command frame. The Target devicecompletes an I/O by sending a Response frame. Any Initiator device mayhave up to 256 active I/O commands at a given time. Before any frame issent, a connection is established between two SAS devices. A connectionconsists of an “Open Address” frame with a WWN field in it. On everyOpen Address, the receiving device compares the Open Address WWN to openI/O commands. Also, every I/O command may have multiple connections.

Typically, storage controllers use a Micro Controller that is 8-bitwide. The foregoing process of tracking connections using the 64-bit WWNaddresses is time consuming. Therefore, there is a need for a system andmethod for efficiently manage connections and effectively use the WWNaddresses.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method for managing framesentering or leaving a storage controller is provided. The methodincludes, comparing frame elements of incoming frames, including aunique World Wide Name (WWN) address with a WWN module entry; and ifthere is a match, updating a counter value for a connection between thestorage controller and a device sending frames. A WWN index value isprovided to a processor of the storage controller. The counter value isincreased when a command frame is received and decreased when a commandis executed and a response is sent to the device.

In yet another aspect of the present invention, a storage controller fortransferring data between a host and a Serial Attached Small ComputerInterface (“SAS”) device is provided. The storage controller includes: aWorld Wide Name (“WWN”) module that includes a table having pluralentries, wherein each row includes a WWN address, an initiator tag valuefield, and an input/output counter value that tracks plural commands fora connection. The WWN module uses the WWN index value that represents anaddress of a row having plural entries.

The WWN module is a part of a link module that interfaces between atransport module and a physical module for transferring information. TheWWN index value is smaller than the WWN address and can be read by amicro-controller or processor of the storage controller.

In yet another aspect of the present invention, a WWN module in astorage controller is provided. The WWN module includes, a table havingplural entries, wherein each row includes a WWN address, an initiatortag value field, and an input/output counter value that tracks pluralcommands for a connection.

This brief summary has been provided so that the nature of the inventionmay be understood quickly. A more complete understanding of theinvention can be obtained by reference to the following detaileddescription of the preferred embodiments thereof concerning the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and other features of the present invention willnow be described with reference to the drawings of a preferredembodiment. In the drawings, the same components have the same referencenumerals. The illustrated embodiment is intended to illustrate, but notto limit the invention. The drawings include the following Figures:

FIG. 1A shows an example of a storage drive system used with theadaptive aspects of the present invention;

FIG. 1B shows a block diagram of a SAS module used in a controller,according to one aspect of the present invention;

FIG. 1C shows a detailed block diagram of a SAS module, according to oneaspect of the present invention;

FIG. 1D shows a SAS frame that is received/transmitted using the SASmodule according to one aspect of the present invention;

FIG. 2A shows a block diagram of a WWN Index module, according to oneaspect of the present invention;

FIG. 2B shows yet another block diagram of a WWN Index module withplural commands, according to one aspect of the present invention;

FIGS. 3A-3G illustrate the various process steps for implementing theWWN index module, according to one aspect of the present invention; and

FIG. 4 is a process flow diagram for using the WWN index module,according to one aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Controller Overview

To facilitate an understanding of the preferred embodiment, the generalarchitecture and operation of a controller will initially be described.The specific architecture and operation of the preferred embodiment willthen be described with reference to the general architecture.

FIG. 1A shows an example of a storage drive system (with an optical diskor tape drive), included in (or coupled to) a computer system. The hostcomputer (not shown) and the storage device 110 (also referred to asdisk 110) communicate via a port using a disk formatter “DF” 104. In analternate embodiment (not shown), the storage device 110 is an externalstorage device, which is connected to the host computer via a data bus.The data bus, for example, is a bus in accordance with a Small ComputerSystem Interface (SCSI) specification. Those skilled in the art willappreciate that other communication buses known in the art can be usedto transfer data between the drive and the host system.

As shown in FIG. 1A, the system includes controller 101, which iscoupled to buffer memory 111 and microprocessor 100. Interface 109serves to couple microprocessor bus 107 to microprocessor 100 and amicro-controller 102 and facilitates transfer of data, address, timingand control information. A read only memory (“ROM”) omitted from thedrawing is used to store firmware code executed by microprocessor 100.

Controller 101 can be an integrated circuit (IC) that comprises ofvarious functional modules, which provide for the writing and reading ofdata stored on storage device 110. Buffer memory 111 is coupled tocontroller 101 via ports to facilitate transfer of data, timing andaddress information. Buffer memory 111 may be a double data ratesynchronous dynamic random access memory (“DDR-SDRAM”) or synchronousdynamic random access memory (“SDRAM”), or any other type of memory.

Disk formatter 104 is connected to microprocessor bus 107 and to buffercontroller 108. A direct memory access (“DMA”) DMA interface (not shown)is connected to microprocessor bus 107 and to data and control port (notshown).

Buffer controller (also referred to as “BC”) 108 connects buffer memory111, channel one (CH1) logic 105, error correction code (“ECC”) module106 to bus 107. Buffer controller 108 regulates data movement into andout of buffer memory 111.

CH1 logic 105 is functionally coupled to SAS module 103 that isdescribed below in detail. CH1 Logic 105 interfaces between buffermemory 111 and SAS module 103. SAS module 103 interfaces with hostinterface 104A to transfer data to and from disk 110.

Data flow between a host and disk passes through buffer memory 111 viachannel 0 (CH0) logic 106A. ECC module 106 generates ECC that is savedon disk 110 during a write operation and provides correction mask to BC108 for disk 110 read operation.

The Channels, CH0 106A, CH1 105 and Channel 2 (not shown) are grantedarbitration turns when they are allowed access to buffer memory 111 inhigh speed burst write or read operations for a certain number ofclocks. The channels use first-in-first out (“FIFO”) type memories tostore data that is in transit. Firmware running on processor 100 canaccess the channels based on bandwidth and other requirements.

To read data from device 110, a host system sends a read command tocontroller 101, which stores the read commands in buffer memory 111.Microprocessor 100 then reads the command out of buffer memory 111 andinitializes the various functional blocks of controller 101. Data isread from device 110 and is passed to buffer controller 108.

To write data, a host system sends a write command to disk controller101, which is stored in buffer 111. Microprocessor 100 reads the commandout of buffer 111 and sets up the appropriate registers. Data istransferred from the host and is first stored in buffer 111, beforebeing written to disk 110. Cyclic redundancy code (“CRC”) values arecalculated based on a logical block address (“LBA”) for the sector beingwritten. Data is read out of buffer 111, appended with ECC code andwritten to disk 110.

Frame Structure:

FIG. 1D shows a SAS frame 129 that is received/transmitted using SASmodule 103. Frame 129 includes a WWW address 129A, a start of frame(“SOF”) value 129G, a frame header 129B that includes a frame type field129E, payload/data 129C, CRC value 129D and end of frame (“EOF”) 129F.WWN address 129A is used for each open connection at a given time.

Also, a frame may be an interlock or non-interlocked, specified by field129E. For an interlock frame, acknowledgement from a host is requiredfor further processing, after the frame is sent to the host.Non-interlock frames are passed through to a host without hostacknowledgement (up to 256 frames per the SAS standard).

SAS Module 103:

FIG. 1B shows a top level block diagram for SAS module 103 used incontroller 101. SAS module 103 includes a physical (“PHY”) module 112, alink module 113 and a transport module (“TRN”) 114 described below indetail. A micro-controller 115 is used to co-ordinate operations betweenthe various modules. A SAS interface 116 is also provided to the PHYmodule 112 for interfacing with a host and interface 117 is used toinitialize the PHY module 112.

FIG. 1C shows a detailed block diagram of SAS module 103 with varioussub-modules. Incoming data 112C is received from a host system, whileoutgoing data 112D is sent to a host system or another device/component.

PHY Module 112:

PHY module 112 includes a serial/deserializer (“SERDES”) 112A thatserializes encoded data for transmission (112D), and de-serializesreceived data (112C). SERDES 112A also recovers a clock signal fromincoming data stream 112C and performs word alignment.

PHY control module 112B controls SERDES 112A and provides the functionsrequired by the SATA standard.

Link Module 113:

Link module 113 opens and closes connections, exchanges identity frames,maintains ACK/NAK (i.e. acknowledged/not acknowledged) balance andprovides credit control. As shown in FIG. 1C, link module 113 has areceive path 118 that receives incoming frames 112C and a transmit path120 that assists in transmitting information 112D. Addresses 121 and 122are used for received and transmitted data, respectively. WWN indexmodule 119A is used for maintaining plural connections states, describedbelow in detail.

Receive path 118 includes a converter 118C for converting 10-bit data to8-bit data, an elasticity buffer/primitive detect segment 118B thattransfers data from a receive clock domain to a transmit block domainand decodes primitives. Descrambler module 118A unscrambles data andchecks for cyclic redundancy check code (“CRC”).

Transmit path 120 includes a scrambler 120A that generates CRC andscrambles (encodes) outgoing data; and primitive mixer module 120B thatgenerates primitives required by SAS protocol/standard and multiplexesthe primitives with the outgoing data. Converter 120C converts 8-bitdata to 10-bit format.

Link module 113 uses plural state machines 119 to achieve the variousfunctions of its sub-components. State machines 119 includes a receivestate machine for processing receive frames, a transmit state machinefor processing transmit frames, a connection state machine forperforming various connection related functions and an initializationstate machine that becomes active after an initialization request orreset.

Transport Module 114:

Transport module 114 interfaces with CH1 105 and link module 113. Intransmit mode, TRN module 114 receives data from CH 1 105, loads thedata (with fibre channel header (FCP) 127) in FIFO 125 and sends data toLink module 113 encapsulated with a header (129B) and a CRC value(129D). In receive mode, TRN MODULE 114 receives data from link module113 (in FIFO 124), and re-packages data (extracts header 126 and 128)before being sent to CH 1105. CH1 105 then writes the data to buffer111. State machine 123 is used to co-ordinate data transfer in thereceive and transmit paths.

WWN Index Module 119A

WWN Index module 119A, as shown in FIG. 2A, includes a table with “n”(where n is greater than 1) elements. WWN Index module 119A storesinformation about each open connection between storage controller 101and a device/host. WWN Index module 119A has plural rows/layers. Eachrow (for example, row 206 in FIG. 2A) is referred to by its WWN indexvalue (address value) 205. For example, row 206 includes a SAS addressfield (64 bit WWN address) 200, an Initiator Connection tag (16 bits)201, an I/O counter (10 bits) 202, a single bit (“V”) 203 to indicatethe validity of an entry and a fresh (F) field 204 that indicates thelatest row that is being serviced.

When an Open Address frame is received, the WWN address 129A (WWNaddress field) of the received frame is compared with the WWN addressfield (200) in module 119A. A successful comparison returns a WWN indexvalue 205. This WWN index value 205 is provided to MC 115. Since the WWNindex value 205 is an 8-bit field, MC 115 can handle it veryefficiently.

It is noteworthy that the present invention is not limited to anyparticular size of module 119A or any of its entries. For example, WWNindex value 205 is not limited to an 8-bit value or any other size.

If a WWN address of an Open Address frame is not recognized by module119A entries and the first frame is of Command type, then a new entry(or row 206) is created and its I/O count 202 is set to one. The new row206 is allocated a WWN index value 205, so that when a frame from thesame source/connection arrives again, then module 119A can return theproper WWN index value (205) after the comparison.

For each frame crossing link module 113, the frame type is checked. Ifthe frame is of Command type, the I/O counter of the active entry isincremented (increased) (202). If the frame is of Response type, the I/Ocount of the active entry is decremented (decreased). When the I/O countreaches zero, the valid bit 203 is reset and the entry becomes vacant.

FIG. 2B shows a detailed diagram of WWN module 119A with row 206. Thevarious entries are loaded in rows based on receive access (path) 207and transmit access (path) 208. Reset command 209 is used to resetmodule 119A. MC 102, MC 115 or MP 100 may issue the reset command.

“Get Index by WWN” 213 (or signal 213) allows searching of module 119Aby WWN address 200 and/or Initiator Tag value 201. MC 115, MC 102 or MP100 may use this function. If the “Get Index by WWN” function 213 findsan entry that matches a search term (for example, for an incomingframe), then the WWN index value 205 is returned with a “success” flag.If no match is found then a new entry is allocated and the new value isreturned. If the table is full based on signal 213, then a “fail” flagis returned. A successful allocation causes the valid bit 203 to be set.The valid bit 203 is cleared fro an entry when the I/O counter value 202reaches a certain value, for example, 0.

Signal/command “INC by Index” 212 is used to increment the index value205. Also, MP 100 (or MC 102 or 115) may load a row (for example, 206)by using an index value 205 (by using “Load by Index” command 211).Using “Clear by Index” signal/command 210 clears entries in a row (206).

FIG. 4 shows a flow diagram for using module 119A, according to oneaspect of the present invention. Turning in detail to FIG. 4, in stepS400, a request to open connection is made between a device (SAS peerdevice) 300A (FIG. 3A) and controller 101. If the request is accepted,then a connection is established in step S401, otherwise the processloops back to step S400 and waits. The connection is shown as 301A inFIG. 3A. At this stage the I/O counter value is zero (shown as 202A).

In step S402, the process determines if a WWN address entry exists. Ifyes, the process moves to step S404. If an entry does not exist in stepS402, then an entry is created in step S403.

In step S404, a WWN index value is established for the entry (WWN indexvalue 205).

In step S405, a frame is received/transmitted by controller 101.

In step S406, the process determines if a frame is of command type. Ifyes, then I/O counter value 202 is incremented (202B, FIG. 3B). If theframe is not of command type, then in step S408, the process determinesif the frame is of response type. If the frame is of a response type,then the I/O counter value 202 is decremented (202B, FIG. 3F).

If the frame is not of a response type (in step S410), then theconnection is closed in step S410 and in step S411, all the entries arede-allocated with the I/O counter value 202 cleared to zero (202A, FIG.3A).

FIGS. 3A-3G illustrate the use of WWN module 119A, according to oneaspect of the present invention. FIG. 3A shows that a connection 301A isestablished between controller 101 and device 300A. I/O counter value iszero, shown as 202A. FIG. 3B shows that a command 300 is received andthereafter, the I/O counter value is increased to 1 (shown as 202B).

FIG. 3C shows that data 301 is received from device 300A and I/O countervalue remains the same (i.e. 1). FIG. 3D shows that controller 101receives another command 302 and that device 300A is ready for atransfer (shown as 300B). The I/O counter value is increased to 2, shownas 202C.

FIG. 3E shows that data 304 is received by device 300A via controller101 and data 303 is received from device 300A. I/O counter value remains2 (shown as 202C).

FIG. 3F shows that command 300 is complete and a response 305 isreceived by device 300A. I/O counter value is decreased to 1 and isshown as 202B.

FIG. 3G shows that data 306 is received by device 300A via controller101. After command 302 is complete, response 307 is sent to device 300A.Thereafter, the I/O counter value is decreased to zero, shown as 202A.

In one aspect of the present invention, a dynamic WWN module is providedthat dynamically updates connection information. Also, the WWN moduleprovides an easy to use index value that can be used by MC 115, MC 102and MP 100.

Although the present invention has been described with reference tospecific embodiments, these embodiments are illustrative only and notlimiting. Many other applications and embodiments of the presentinvention will be apparent in light of this disclosure.

1. A storage controller that transfers data between a host and a storagedevice, the storage controller comprising: an interface module thatprovides an interface between a plurality of devices including the hostand the storage controller; and an index module that: stores a pluralityof entries that correspond to each of the plurality of devices; receivesa frame of data including a world wide name (WWN) address; compares theWWN address to the plurality of entries; and generates an index value ofthe plurality of entries when the WWN address matches one of theplurality of entries.
 2. The storage controller of claim 1, wherein theinterface module includes a Serial Attached Small Computer Interface(SAS) module.
 3. The storage controller of claim 1, wherein the storagecontroller communicates with one of the plurality of devices based onthe match.
 4. The storage controller of claim 1, wherein: the WWNaddress has a first length and the index value has a second length; andthe second length is less than the first length.
 5. The storagecontroller of claim 4, wherein the first length is 64 bits and thesecond length is 8 bits.
 6. The storage controller of claim 1, whereinthe index module includes a World Wide Name (WWN) module.
 7. The storagecontroller of claim 1, wherein the index module updates a counter valuebased on the match.
 8. The storage controller of claim 1, wherein theindex module generates a new entry and a respective index value when theWWN address does not match one of the plurality of entries.
 9. Thestorage controller of claim 1, wherein the index module stores theplurality of entries in a table including a plurality of rows.
 10. Astorage controller that transfers data between a host and a storagedevice, the storage controller comprising: interfacing means forproviding an interface between a plurality of devices including the hostand the storage controller; and indexing means for: storing a pluralityof entries that correspond to each of the plurality of devices;receiving a frame of data including a world wide name (WWN) address;comparing the WWN address to the plurality of entries; and generating anindex value of the plurality of entries when the WWN address matches oneof the plurality of entries.
 11. The storage controller of claim 10,wherein the interfacing means includes a Serial Attached Small ComputerInterface (SAS) module.
 12. The storage controller of claim 10, whereinthe storage controller communicates with one of the plurality of devicesbased on the match.
 13. The storage controller of claim 10, wherein: theWWN address has a first length and the index value has a second length;and the second length is less than the first length.
 14. The storagecontroller of claim 13, wherein the first length is 64 bits and thesecond length is 8 bits.
 15. The storage controller of claim 10, whereinthe indexing means includes a World Wide Name (WWN) module.
 16. Thestorage controller of claim 10, wherein the indexing means updates acounter value based on the match.
 17. The storage controller of claim10, wherein the indexing means generates a new entry and a respectiveindex value when the WWN address does not match one of the plurality ofentries.
 18. The storage controller of claim 10, wherein the indexingmeans stores the plurality of entries in a table including a pluralityof rows.
 19. A method for managing frames of data in a storagecontroller, the method comprising: providing an interface between aplurality of devices including a host and the storage controller;storing a plurality of entries each corresponding to one of theplurality of devices; receiving a frame of data including a world widename (WWN) address; comparing the WWN address to the plurality ofentries; and generating an index value of the plurality of entries whenthe WWN address matches one of the plurality of entries.
 20. The methodof claim 19, wherein providing the interface includes providing a SerialAttached Small Computer Interface (SAS) module.
 21. The method of claim19, further comprising communicating with one of the plurality ofdevices based on the match.
 22. The method of claim 19, wherein: the WWNaddress has a first length and the index value has a second length; andthe second length is less than the first length.
 23. The method of claim22, wherein the first length is 64 bits and the second length is 8 bits.24. The method of claim 20, wherein the SAS module includes a World WideName (WWN) module.
 25. The method of claim 19, further comprisingupdating a counter value based on the match.
 26. The method of claim 19,further comprising generating a new entry and a respective index valuewhen the WWN address does not match one of the plurality of entries. 27.The method of claim 19, further comprising storing the plurality ofentries in a table including a plurality of rows.
 28. The storagecontroller of claim 1, wherein each of the index values identifies aplurality of entries.
 29. The storage controller of claim 1, wherein theplurality of entries for each of the plurality of devices includes anaddress, a tag, and a counter.
 30. The storage controller of claim 1,wherein the plurality of entries for each of the plurality of devicesinclude a device identifying address.
 31. A storage controller thattransfers data between a host and a storage device, the storagecontroller comprising: an interface module that provides an interfacebetween a plurality of devices including the host and the storagecontroller; and an index module that: stores a plurality of entries thatcorrespond to each of the plurality of devices; receives a frame of dataincluding an address, that compares the address to the plurality ofentries; and generates an index value of the plurality of entries whenthe address matches one of the plurality of entries, wherein: theplurality of entries for each of the plurality of devices includes acounter; and the counter indicates a number of open connections betweenthe host and one of the plurality of devices.
 32. The storage controllerof claim 1, wherein the index module compares a received address withaddresses of the plurality of entries and provide one of the indexvalues when there is a match.
 33. The storage controller of claim 1,wherein the plurality of entries comprise connection informationassociated with connections between the storage device and the pluralityof devices.
 34. A storage controller that transfers data between a hostand a storage device, the storage controller comprising: an interfacemodule that provides an interface between a plurality of devicesincluding the host and the storage controller; and an index module that:stores a plurality of entries that correspond to each of the pluralityof devices; receives a frame of data including an address, that comparesthe address to the plurality of entries; and generates an index value ofthe plurality of entries when the address matches one of the pluralityof entries, wherein the plurality of entries for each of the pluralityof devices includes at least one of a counter value, an initiator tag, avalidity value, and a latest row serviced value.
 35. The storagecontroller of claim 34, wherein the index module increments the countervalue for a target device associated with the received frame when theaddress matches one of the plurality of entries.
 36. The storagecontroller of claim 34, wherein the index module creates a new set ofentries for a target device associated with the received frame when theaddress does not match one of the plurality of entries.
 37. The storagecontroller of claim 36, wherein the index module initiates the countervalue for a target device associated with the received frame when theaddress does not match one of the plurality of entries.
 38. The storagecontroller of claim 34, wherein the counter value is increased when acommand frame is received and decreased when a command is executed and aresponse is sent to the device.
 39. The storage controller of claim 34,wherein the plurality of entries for each of the plurality of devicesincludes a counter value and at least one of the initiator tag, thevalidity value, and the latest row serviced value.